Beta-L-2&#39;-deoxy-nucleosides for the treatment of HIV infection

ABSTRACT

Compounds and pharmaceutical compositions active against HIV are provided, as is a method for the treatment of HIV infection in humans and other host animals is provided comprising administering an effective amount of a β-L-(2′ or 3′-azido)-2′,3′-dideoxy-5-fluorocytosine of the formula  
                 
 
     wherein R is H, acyl, monophosphate, diphosphate, or triphosphate, or a stabilized phosphate derivative (to form a stabilized nucleotide prodrug), and R′ is H, acyl, or alkyl.

BACKGROUND OF THE INVENTION

[0001] This invention is in the area of methods for the treatment ofhuman immunodeficiency virus (also referred to as “HIV”) that includesadministering to a host in need thereof, either alone or in combination,an effective HIV-treatment amount of one or more of the active compoundsdisclosed herein, or a pharmaceutically acceptable prodrug or salt ofone of these compounds. This application claims priority to U.S. Ser.No. 60/107,178, filed on Nov. 5, 1998, and U.S. Ser. No. 60/115,862,filed on Jan. 13, 1999.

[0002] In 1981, acquired immune deficiency syndrome (AIDS) wasidentified as a disease that severely compromises the human immunesystem, and that almost without exception leads to death. In 1983, theetiological cause of AIDS was determined to be the humanimmunodeficiency virus (HIV).

[0003] In 1985, it was reported that the synthetic nucleoside3′-azido-3′-deoxythymidine (AZT) inhibits the replication of humanimmunodeficiency virus. Since then, a number of other syntheticnucleosides, including (−)-β-2′,3′-dideoxy-3′-thiacytidine (3TC),β-2′,3′-dideoxy-3′-thia-5-fluorocytidine (FTC), 2′,3′-dideoxyinosine(DDI), 2′,3′-dideoxycytidine (DDC), and2′,3′-dideoxy-2′,3′-didehydrothymidine (D4T), have been proven to beeffective against HIV. After cellular phosphorylation to the5′-triphosphate by cellular kinases, these synthetic nucleosides areincorporated into a growing strand of viral DNA, causing chaintermination due to the absence of the 3′-hydroxyl group. They can alsoinhibit the viral enzyme reverse transcriptase.

[0004] The success of various synthetic nucleosides in inhibiting thereplication of HIV in vivo or in vitro has led a number of researchersto design and test nucleosides that substitute a heteroatom for thecarbon atom at the 3′-position of the nucleoside. European PatentApplication Publication No. 0 337 713 and U.S. Pat. No. 5,041,449,assigned to BioChem Pharma, Inc., disclose racemic2-substituted-4-substituted-1,3-dioxolanes that exhibit antiviralactivity. U.S. Pat. No. 5,047,407 and European Patent ApplicationPublication No. 0 382 526, also assigned to BioChem Pharma, Inc.,disclose that a number of racemic2-substituted-5-substituted-1,3-oxathiolane nucleosides have antiviralactivity, and specifically report that the racemic mixture of2-hydroxymethyl-5-(cytosin-1-yl)-1,3-oxathiolane (referred to asBCH-189) has approximately the same activity against HIV as AZT, withlittle toxicity. The (−)-enantiomer of the racemate BCH-189, known as3TC, which is covered by U.S. Pat. No. 5,539,116 to Liotta et al., iscurrently sold for the treatment of HIV in humans in the U.S. incombination with AZT.

[0005] It has also been disclosed thatcis-2-hydroxymethyl-5-(5-fluorocytosin-1-yl)-1,3-oxathiolane (“FTC”) haspotent HIV activity. Schinazi, et al., “Selective Inhibition of HumanImmunodeficiency viruses by Racemates and Enantiomers ofcis-5-Fluoro-1-[2-(Hydroxymethyl)-1,3-Oxathiolane-5-yl]Cytosine”Antimicrobial Agents and Chemotherapy, November 1992, pp. 2423-2431. Seealso U.S. Pat. Nos. 5,210,085; 5,814,639; 5,728,575; 5,827,727;5,914,331; WO 91/11186 and WO 92/14743.

[0006] WO 96/40164 filed by Emory University, UAB Research Foundation,and the Centre National de la Recherche Scientifique discloses a numberof β-L-2′,3′-dideoxynucleosides for the treatment of hepatitis B.

[0007] WO 95/07287 also filed by Emory University, UAB ResearchFoundation, and the Centre National de la Recherche Scientifiquediscloses 2′ or 3′ deoxy and 2′,3′-dideoxy-β-L-pentofuranosylnucleosides for the treatment of HIV infection.

[0008] WO96/13512 filed by Genencor International, Inc., and Lipitek,Inc., discloses the preparation of L-ribofuranosyl nucleosides asantitumor agents and virucides.

[0009] WO95/32984 discloses lipid esters of nucleoside monophosphates asimmunosuppresive drugs.

[0010] DE4224737 discloses cytosine nucleosides and their pharmaceuticaluses.

[0011] Tsai, et al., in Biochem. Pharmacol. 48(7), pages 1477-81, 1994discloses the effect of the anti-HIV agent2′-β-D-F-2′,3′-dideoxynucleoside analogs on the cellular content ofmitochondrial DNA and lactate production.

[0012] Galvez, J. Chem. Inf. Comput. Sci. (1994), 35(5), 1198-203describes molecular computation ofβ-D-3′-azido-2′,3′-dideoxy-5-fluorocytidine.

[0013] Mahmoudian, Pharm. Research 8(1), 43-6 (1991) disclosesquantitative structure-activity relationship analyses of HIV agents suchas β-D-3′-azido-2′,3′-dideoxy-5-fluorocytidine.

[0014] U.S. Pat. No. 5,703,058 discloses (5-carboximido or5-fluoro)-(2′,3′-unsaturated or 3′-modified) pyrimidine nucleosides forthe treatment of HIV and HBV infection.

[0015] Lin, et al., discloses the synthesis and antiviral activity ofvarious 3′-azido analogues of β-D-nucleosides in J. Med. Chem. 31(2),336-340 (1988).

[0016] In light of the fact that acquired immune deficiency syndrome andAIDS-related complex have reached epidemic levels worldwide, and havetragic effects on the infected patient, there remains a strong need toprovide new effective pharmaceutical agents to treat these diseases thathave low toxicity to the host.

[0017] It is an object of the present invention to provide a compoundand method for the treatment of human patients or other host animalsinfected with HIV.

SUMMARY OF THE INVENTION

[0018] A method for the treatment of HIV infection in humans and otherhost animals is disclosed that includes administering an effectiveHIV-treatment amount to the host of a β-L-(2′ or3′-azido)-2′,3′-dideoxy-5-fluorocytosine nucleoside or apharmaceutically acceptable salt, ester, or prodrug thereof, including astabilized phosphate, administered either alone or in combination oralternation with another anti-HIV agent, optionally in apharmaceutically acceptable carrier. In a preferred embodiment, the 2′or 3′-azido group is in the ribosyl configuration.

[0019] The disclosed β-L-(2′ or 3′-azido)-2′,3′-dideoxy-5-fluorocytosinenucleosides, or pharmaceutically acceptable salts, esters, or prodrugsor pharmaceutically acceptable formulations containing these compoundsare useful in the prevention and treatment of HIV infections and otherrelated conditions such as Acquired Immune Deficiency Syndrome (AIDS),AIDS-Related Complex (ARC), persistent generalized lymphadenopathy(PGL), AIDS-related neurological conditions, anti-HIV antibody positiveand HIV-positive conditions, Kaposi's sarcoma, thrombocytopenia purpureaand opportunistic infections. These compounds or formulations can alsobe used prophylactically to prevent or retard the progression ofclinical illness in individuals who are anti-HIV antibody or HIV-antigenpositive or who have been exposed to HIV.

[0020] In one embodiment, the active compound isβ-L-(2′-azido)-2′,3′-dideoxy-5-fluorocytosine (L-2′-A-5-FddC) or apharmaceutically acceptable ester, salt or prodrug thereof of theformula:

[0021] wherein R is H, acyl, monophosphate, diphosphate, ortriphosphate, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug), and R′ is H, acyl, or alkyl.

[0022] In another embodiment, the active compound isβ-L-(3′-azido)-2′,3′-dideoxy-5-fluorocytosine (L-3′-A-5-FddC) or apharmaceutically acceptable ester, salt or prodrug thereof of theformula:

[0023] wherein R is H, acyl, monophosphate, diphosphate, ortriphosphate, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug), and R′ is H, acyl, or alkyl.

[0024] In another embodiment, the L-(2′ or 3′)-A-5-FddC nucleoside isadministered in alternation or combination with one or more othercompounds which exhibit activity against HIV, as described in moredetail below. In general, during alternation therapy, an effectivedosage of each agent is administered serially, whereas in combinationtherapy, an effective dosage of two or more agents are administeredtogether. The dosages will depend on absorption, inactivation, andexcretion rates of the drug as well as other factors known to those ofskill in the art. It is to be noted that dosage values will also varywith the severity of the condition to be alleviated. It is to be furtherunderstood that for any particular subject, specific dosage regimens andschedules should be adjusted over time according to the individual needand the professional judgment of the person administering or supervisingthe administration of the compositions. In one preferred embodiment, thecompound is administered in combination with AZDU(3′-azido-2′,3′-dideoxyuridine).

BRIEF DESCRIPTION OF THE FIGURES

[0025]FIG. 1 is an illustration of a general reaction scheme for thestereospecific synthesis of 3′-substituted β-L-^(dideoxynucleosides).

[0026]FIG. 2 is an illustration of a general reaction scheme for thestereospecific synthesis of 2′-substituted β-L-^(dideoxynucleosides).

[0027]FIG. 3 is an illustration of one process for the preparation ofβ-L-(3′-azido)-2′,3′-dideoxy-5-fluorocytosine (L-3′-A-5-FddC).

[0028]FIG. 4 is an illustration of one process for the preparation ofβ-L-(2′-azido)-2′,3′-dideoxy-5-fluorocytidine (L-2′-A-5-FddC).

DETAILED DESCRIPTION OF THE INVENTION

[0029] A method for the treatment of HIV infection in humans and otherhost animals is disclosed that includes administering an effectiveamount of a β-L-(2′ or 3′-azido)-2′,3′-dideoxy-5-fluorocytosinenucleoside (referred to below as “L-(2′ or 3′)-A-5-FddC”) or apharmaceutically acceptable salt, ester, or prodrug thereof, including astabilized phosphate, either alone or in combination or alternation withanother anti-HIV agent, optionally in a pharmaceutically acceptablecarrier.

[0030] The compounds described herein can be used to treat AIDS andAIDS-related conditions including Acquired Immune Deficiency Syndrome(AIDS), AIDS-Related Complex (ARC), persistent generalizedlymphadenopathy (PGL), AIDS-related neurological conditions, anti-HIVantibody positive and HIV-positive conditions, Kaposi's sarcoma,thrombocytopenia purpurea and opportunistic infections. The method ofthe present invention includes the use of an L-(2′ or 3′)-A-5-FddCprophylactically to prevent or retard the progression of clinicalillness in individuals who are anti-HIV antibody or HIV-antigen positiveor who have been exposed to HIV.

[0031] As used herein, the term “substantially in the form of a singleisomer” “substantially free of” or “substantially in the absence of”refers to a nucleoside that is at least approximately 95% in thedesignated stereoconfiguration.

[0032] The term alkyl, as used herein, unless otherwise specified,refers to a saturated straight, branched, or cyclic, primary, secondary,or tertiary hydrocarbon of C₁ to C₁₀, and specifically includes methyl,ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, cylcobutyl,cyclopropyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl,cyclohexyl, cyclohexylmethyl, 3-methylpentyl, 2,2-dimethylbutyl, and2,3-dimethylbutyl. The alkyl group can be optionally substituted withone or more moieties selected from the group consisting of hydroxyl,amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonicacid, sulfate, phosphonic acid, phosphate, or phosphonate, eitherunprotected, or protected as necessary, as known to those skilled in theart, for example, as taught in Greene, et al., “Protective Groups inOrganic Synthesis,” John Wiley and Sons, Second Edition, 1991. The termlower alkyl, as used herein, and unless otherwise specified, refers to aC₁ to C₄ ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl,sec-butyl, or t-butyl groupAs used herein, the term acyl refers tomoiety of the formula —C(O)R′, wherein R′ is alkyl; aryl, alkaryl,aralkyl, heteroaromatic, alkoxyalkyl including methoxymethyl; arylalkylincluding benzyl; aryloxyalkyl such as phenoxymethyl; aryl includingphenyl optionally substituted with halogen, C₁ to C₄ alkyl or C₁ to C₄alkoxy, or the residue of an amino acid. The term acyl specificallyincludes but is not limited to acetyl, propionyl, butyryl, pentanoyl,3-methylbutyryl, hydrogen succinate, 3-chlorobenzoate, benzoyl, acetyl,pivaloyl, mesylate, propionyl, valeryl, caproic, caprylic, capric,lauric, myristic, palmitic, stearic, and oleic.

[0033] The L-(2′ or 3′)-A-5-FddC nucleoside can be converted into apharmaceutically acceptable ester by reaction with an appropriateesterifying agent, for example, an acid halide or anhydride. Thenucleoside or its pharmaceutically acceptable prodrug can be convertedinto a pharmaceutically acceptable salt thereof in a conventionalmanner, for example, by treatment with an appropriate base or acid. Theester or salt can be converted into the parent nucleoside, for example,by hydrolysis.

[0034] As used herein, the term pharmaceutically acceptable salts orcomplexes refers to salts or complexes of the L-(2′ or 3′)-A-5-FddC thatretain the desired biological activity of the parent compound andexhibit minimal, if any, undesired toxicological effects. Nonlimitingexamples of such salts are (a) acid addition salts formed with inorganicacids (for example, hydrochloric acid, hydrobromic acid, sulfuric acid,phosphoric acid, nitric acid, and the like), and salts formed withorganic acids such as acetic acid, oxalic acid, tartaric acid, succinicacid, malic acid, ascorbic acid, benzoic acid, tannic acid, pamoic acid,alginic acid, polyglutamic acid, naphthalenesulfonic acids,naphthalenedisulfonic acids, and polygalacturonic acid; (b) baseaddition salts formed with cations such as sodium, potassium, zinc,calcium, bismuth, barium, magnesium, aluminum, copper, cobalt, nickel,cadmium, sodium, potassium, and the like, or with an organic cationformed from N,N-dibenzylethylene-diamine, ammonium, or ethylenediamine;or (c) combinations of (a) and (b); e.g., a zinc tannate salt or thelike.

[0035] The term prodrug, as used herein, refers to a compound that isconverted into the nucleoside on administration in vivo, or that hasactivity in itself. Nonlimiting examples are pharmaceutically acceptablesalts (alternatively referred to as “physiologically acceptable salts”),and the 5′ and N⁴ acylated or alkylated derivatives of the activecompound, as well as the 5′-monophosphate, diphosphate, or triphosphatederivatives or stablized phophate prodrugs (alternatively referred to as“physiologically or pharmaceutically acceptable derivatives”) orphosphate lipid prodrugs, as described herein.

[0036] Modifications of the active compounds, specifically at the N⁴ and5′-O positions, can affect the bioavailability and rate of metabolism ofthe active species, thus providing control over the delivery of theactive species.

[0037] A preferred embodiment of the present invention is a method forthe treatment of HIV infections in humans or other host animals, thatincludes administering an effective amount of one or more of an L-(2′ or3′)-A-5-FddC nucleoside selected from the group consisting of,L-2′-A-5-FddC, and L-3′-A-5-FddC, or a physiologically acceptableprodrug thereof, including a phosphate, 5′ and or N⁴ alkylated oracylated derivative, or a physiologically acceptable salt thereof,optionally in a pharmaceutically acceptable carrier. The compounds ofthis invention either possess anti-HIV activity, or are metabolized to acompound or compounds that exhibit anti-HIV activity. In a preferredembodiment, the L-(2′ or 3′)-A-5-FddC nucleoside is administeredsubstantially in the form of a single isomer, i.e., at leastapproximately 95% in the designated stereoconfiguration.

[0038] Combination or Alternation Therapy

[0039] It has been recognized that drug-resistant variants of HIV canemerge after prolonged treatment with an antiviral agent. Drugresistance most typically occurs by mutation of a gene that encodes foran enzyme used in the viral life cycle. Recently, it has beendemonstrated that the efficacy of a drug against HIV infection can beprolonged, augmented, or restored by administering the compound incombination or alternation with a second, and perhaps third, antiviralcompound that induces a different mutation from that caused by theprinciple drug. Alternatively, the pharmacokinetics, biodistribution, orother parameter of the drug can be altered by such combination oralternation therapy. In general, combination therapy is typicallypreferred over alternation therapy because it induces multiplesimultaneous stresses on the virus.

[0040] The second antiviral agent for the treatment of HIV, in oneembodiment, can be a reverse transcriptase inhibitor (a “RTI”), whichcan be either a synthetic nucleoside (a “NRTI”) or a non-nucleosidecompound (a “NNRTI”). In an alternative embodiment, in the case of HIV,the second (or third) antiviral agent can be a protease inhibitor. Inother embodiments, the second (or third) compound can be a pyrophosphateanalog, or a fusion binding inhibitor. A list compiling resistance datacollected in vitro and in vivo for a number of antiviral compounds isfound in Schinazi, et al, Mutations in retroviral genes associated withdrug resistance, International Antiviral News, Volume 1(4),International Medical Press 1996.

[0041] Preferred examples of antiviral agents that can be used incombination or alternation with the compounds disclosed herein for HIVtherapy include 2-hydroxymethyl-5-(5-fluorocytosin-1-yl)-1,3-oxathiolane(FTC); the (−)-enantiomer of2-hydroxymethyl-5-(cytosin-1-yl)-1,3-oxathiolane (3TC); carbovir,acyclovir, interferon, AZT, DDI, DDC, D4T, CS-92(3′-azido-2′,3′-dideoxy-5-methyl-cytidine), and β-D-dioxolanenucleosides such as β-D-dioxolanyl-guanine (DXG),β-D-dioxolanyl-2,6-diaminopurine (DAPD), andβ-D-dioxolanyl-6-chloropurine (ACP), MKC-442(6-benzyl-1-(ethoxymethyl)-5-isopropyl uracil.

[0042] Preferred protease inhibitors include crixovan (Merck),nelfinavir (Agouron), ritonavir (Abbot), saquinavir (Roche), and DMP-450(DuPont Merck).

[0043] Nonlimiting examples of compounds that can be administered incombination or alternation with any of the β-L-(2′ or3′-azido)-2′,3′-dideoxy-5-fluorocytosines of the present inventioninclude(1S,4R)-4-[2-amino-6-cyclopropyl-amino)-9H-purin-9-yl]-2-cyclopentene-1-methanolsuccinate (“1592”, a carbovir analog; Glaxo Wellcome); 3TC:(−)-β-L-2′,3′-dideoxy-3′-thiacytidine (Glaxo Wellcome); a-APAR18893:a-nitro-anilino-phenylacetamide; A-77003; C2 symmetry-basedprotease inhibitor (Abbott); A-75925: C2 symmetry-based proteaseinhibitor (Abbott); AAP-BHAP: bisheteroarylpiperazine analog (Upjohn);ABT-538: C2 symmetry-based protease inhibitor (Abbott); AzddU:3′-azido-2′,3′-dideoxyuridine; AZT: 3′-azido-3′-deoxythymidine (GlaxoWellcome); AZT-p-ddI:3′-azido-3′-deoxythymidilyl-(5′,5′)-2′,3′-dideoxyinosinic acid (Ivax);BHAP: bisheteroarylpiperazine; BILA 1906:N-{1S-[[[3-[2S-{(1,1-dimethylethyl)amino]carbonyl}-4R-]3-pyridinylmethyl)thio]-1-piperidinyl]-2R-hydroxy-1S-(phenylmethyl)-propyl]amino]carbonyl]-2-methylpropyl}-2-quinolinecarboxamide(Bio Mega/Boehringer-Ingelheim); BILA 2185:N-(1,1-dimethylethyl)-1-[2S-[[2-2,6-dimethyphenoxy)-1-oxoethyl]amino]-2R-hydroxy-4-phenylbutyl]4R-pyridinylthio)-2-piperidinecarboxamide(Bio Mega/Boehringer-Ingelheim); BM+51.0836: thiazolo-isoindolinonederivative; BMS 186,318: aminodiol derivative HIV-1 protease inhibitor(Bristol-Myers-Squibb); d4API:9-[2,5-dihydro-5-(phosphonomethoxy)-2-furanel]adenine (Gilead); d4C:2′,3′-didehydro-2′,3′-dideoxycytidine; d4T:2′,3′-didehydro-3′-deoxythymidine (Bristol-Myers-Squibb); ddC;2′,3′-dideoxycytidine (Roche); ddI: 2′,3′-dideoxyinosine(Bristol-Myers-Squibb); DMP-266: a 1,4-dihydro-2H-3, 1-benzoxazin-2-one;DMP-450:{[4R-(4-a,5-a,6-b,7-b)[-hexahydro-5,6-bis(hydroxy)-1,3-bis(3-amino)phenyl]methyl)-4,7-bis(phenylmethyl)-2H-1,3-diazepin-2-one}-bismesylate(Avid); DXG:(−)-β-D-dioxolane-guanosine (Triangle);EBU-dM:5-ethyl-1-ethoxymethyl-6-(3,5-dimethylbenzyl)uracil; E-EBU:5-ethyl-1-ethoxymethyl-6-benzyluracil; DS: dextran sulfate; E-EPSeU:1-(ethoxymethyl)-(6-phenylselenyl)-5-ethyluracil; E-EPU:1-(ethoxymethyl)-(6-phenyl-thio)-5-ethyluracil; FTC:β-2′,3′-dideoxy-5-fluoro-3′-thiacytidine (Triangle); HBY097:S-4-isopropoxycarbonyl-6-methoxy-3-methylthio-methyl)-3,4-dihydroquinoxalin-2(1H)-thione;HEPT: 1-[(2-hydroxyethoxy)methyl]6-(phenylthio)thymine; HIV-1: humanimmunodeficiency virus type 1; JM2763:1,1′-(1,3-propanediyl)-bis-1,4,8,11-tetraazacyclotetradecane (JohnsonMatthey);JM3100:1,1′-[1,4-phenylenebis-(methylene)]-bis-1,4,8,11-tetraazacyclotetradecane(JohnsonMatthey); KNI-272: (2S,3S)-3-amino-2-hydroxy-4-phenylbutyricacid-containing tripeptide; L-697,593;5-ethyl-6-methyl-3-(2-phthalimido-ethyl)pyridin-2(1H)-one; L-735,524:hydroxy-aminopentane amide HIV-1 protease inhibitor (Merck); L-697,661:3-{[(-4,7-dichloro-1,3-benzoxazol-2-yl)methyl]amino}-5-ethyl-6-methylpyridin-2(1H)-one; L-FDDC: (−)-β-L-5-fluoro-2′,3′-dideoxycytidine;L-FDOC:(−)-β-L-5-fluoro-dioxolane cytosine; MKC442:6-benzyl-1-ethoxymethyl-5-isopropyluracil (I-EBU; Triangle/Mitsubishi);Nevirapine:11-cyclopropyl-5,11-dihydro-4-methyl-6H-dipyridol[3,2-b:2′,3′-e]diazepin-6-one(Boehringer-Ingelheim); NSC648400:1-benzyloxymethyl-5-ethyl-6-(alpha-pyridylthio)uracil (E-BPTU); P9941:[2-pyridylacetyl-IlePheAla-y(CHOH)]2 (Dupont Merck); PFA:phosphonoformate (foscarnet; Astra); PMEA:9-(2-phosphonylmethoxyethyl)adenine (Gilead); PMPA:(R)-9-(2-phosphonyl-methoxypropyl)adenine (Gilead); Ro 31-8959:hydroxyethylamine derivative HIV-1 protease inhibitor (Roche); RPI-312:peptidyl protease inhibitor,1-[(3s)-3-(n-alpha-benzyloxycarbonyl)-1-asparginyl)-amino-2-hydroxy-4-phenylbutyryl]-n-tert-butyl-1-prolineamide; 2720:6-chloro-3,3-dimethyl-4-(isopropenyloxycarbonyl)-3,4-dihydro-quinoxalin-2(1H)thione;SC-52151: hydroxyethylurea isostere protease inhibitor (Searle);SC-55389A: hydroxyethyl-urea isostere protease inhibitor (Searle); TIBOR82150:(+)-(5S)-4,5,6,7-tetrahydro-5-methyl-6-(3-methyl-2-butenyl)imidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-thione(Janssen); TIBO 82913:(+)-(5S)-4,5,6,7,-tetrahydro-9-chloro-5-methyl-6-(3-methyl-2-butenyl)imidazo[4,5,1jk]-[1,4]benzo-diazepin-2(1H)-thione(Janssen); TSAO-m3T:[2′,5′-bis-O-(tert-butyldimethylsilyl)-3′-spiro-5′-(4′-amino-1′,2′-oxathiole-2′,2′-dioxide)]-b-D-pentofuranosyl-N3-methylthymine;U90152:1-[3-[(1-methylethyl)-amino]-2-pyridinyll-4-[[5-[(methylsulphonyl)-amino]-1H-indol-2yl]carbonyl]piperazine;UC: thiocarboxanilide derivatives (Uniroyal);UC-781=N-[4-chloro-3-(3-methyl-2-butenyloxy)phenyl]-2-methyl-3-furancarbothioamide;UC-82=N-[4-chloro-3-(3-methyl-2-butenyloxy)phenyl]-2-methyl-3-thiophenecarbothioamide;VB 11,328: hydroxyethyl-sulphonamide protease inhibitor (Vertex);VX-478: hydroxyethylsulphonamide protease inhibitor (Vertex); XM 323:cyclic urea protease inhibitor (Dupont Merck) or DMP-266 (efavirenz,Sustiva).

[0044] Preparation of the Active Compounds

[0045] Stereochemistry

[0046] Since the 1′ and 4′ carbons of the sugar or dioxolanyl moiety(referred to below generically as the sugar moiety) of the nucleosidesare chiral, their nonhydrogen substituents (CH₂OR and the pyrimidine orpurine base, respectively) can be either cis (on the same side) or trans(on opposite sides) with respect to the sugar ring system. The fouroptical isomers therefore are represented by the followingconfigurations (when orienting the sugar moiety in a horizontal planesuch that the “primary” oxygen (that between the C1′ and C4′-atoms is inback): “β” or “cis” (with both groups “up”, which corresponds to theconfiguration of naturally occurring nucleosides, i.e., the Dconfiguration), “β” or cis (with both groups “down”, which is anonnaturally occurring configuration, i.e., the L configuration), “α”or“trans” (with the C2 substituent “up” and the C5 substituent “down”),and trans (with the C2 substituent “down” and the C5 substituent “up”).

[0047] The active nucleosides of the present invention are in theβ-L-configuration, with the azido group in the ribosyl configuration.

[0048] Nucleotide Prodrugs

[0049] Any of the nucleosides described herein can be administered as astabilized nucleotide prodrug to increase the activity, bioavailability,stability or otherwise alter the properties of the nucleoside. A numberof nucleotide prodrug ligands are known. In general, alkylation,acylation or other lipophilic modification of the mono, di ortriphosphate of the nucleoside will increase the stability of thenucleotide. Examples of substituent groups that can replace one or morehydrogens on the phosphate moiety are alkyl, aryl, steroids,carbohydrates, including sugars, 1,2-diacylglycerol and alcohols. Manyare described in R. Jones and N. Bischofberger, Antiviral Research, 27(1995) 1-17. Any of these can be used in combination with the disclosednucleosides to achieve a desired effect.

[0050] In one embodiment, the L-(2′ or 3′)-A-5-FddC nucleoside isprovided as 5′-hydroxyl lipophilic prodrug, i.e., a 5′-ether lipid or a5′-phosphoether lipid. Nonlimiting examples of U.S. patents thatdisclose suitable lipophilic substituents that can be covalentlyincorporated into the nucleoside, preferably at the 5′-OH position ofthe nucleoside or lipophilic preparations, include U.S. Pat. Nos.5,149,794 (Sep. 22, 1992, Yatvin et al.); 5,194,654 (Mar. 16, 1993,Hostetler et al., 5,223,263 (Jun. 29, 1993, Hostetler et al.); 5,256,641(Oct. 26, 1993, Yatvin et al.); 5,411,947 (May 2, 1995, Hostetler etal.); 5,463,092 (Oct. 31, 1995, Hostetler et al.); 5,543,389 (Aug. 6,1996, Yatvin et al.); 5,543,390 (Aug. 6, 1996, Yatvin et al.); 5,543,391(Aug. 6, 1996, Yatvin et al.); and 5,554,728 (Sep. 10, 1996; Basava etal.), all of which are incorporated herein by reference.

[0051] Foreign patent applications that disclose lipophilic substituentsthat can be attached to the L-(2′ or 3′-A-5-FddC nucleoside derivativeof the present invention, or lipophilic preparations, include WO89/02733, W0 90/00555, W0 91/16920, W0 91/18914, W0 93/00910, W094/26273, W0 96/15132, EP 0 350 287, EP 93917054.4, and W0 91/19721.

[0052] Additional nonlimiting examples of L-(2′ or 3′)-A-5-FddCnucleosides are those that contain substituents as described in thefollowing publications. These derivatized nucleosides can be used forthe indications described in the text or otherwise as antiviral agents,including as anti-HIV agents. Ho, D. H. W. (1973) Distribution of Kinaseand deaminase of 1b-D-arabinofuranosylcytosine in tissues of man andmouse. Cancer Res. 33, 2816-2820; Holy, A. (1993) Isopolarphosphorous-modified nucleotide analogues. In: De Clercq (Ed.), Advancesin Antiviral Drug Design, Vol. I, JAI Press, pp. 179-231; Hong, C. I.,Nechaev, A., and West, C. R. (1979a) Synthesis and antitumor activity of1b-D-arabinofuranosylcytosine conjugates of cortisol and cortisone.Biochem. Biophys. Rs. Commun. 88, 1223-1229; Hong, C. I., Nechaev, A.,Kirisits, A. J. Buchheit, D. J. and West, C. R. (1980) Nucleosideconjugates as potential antitumor agents. 3. Synthesis and antitumoractivity of 1-(b-D-arabinofuranosyl)cytosine conjugates ofcorticosteriods and selected lipophilic alcohols. J. Med. Chem. 28,171-177; Hostetler, K. Y., Stuhmiller, L. M., Lenting, H. B. M. van denBosch, H. and Richman, D. D. (1990) Synthesis and antiretroviralactivity of phospholipid analogs of azidothymidine and other antiviralnucleosides. J. Biol. Chem. 265, 6112-6117; Hostetler, K. Y., Carson, D.A. and Richman, D. D. (1991); Phosphatidylazidothymidine: mechanism ofantiretroviral action in CEM cells. J. Biol. Chem. 266, 11714-11717;Hostetler, K. Y., Korba, B. Sridhar, C., Gardener, M. (1994a) Antiviralactivity of phosphatidyl-dideoxycytidine in hepatitis B-infected cellsand enhanced hepatic uptake in mice. Antiviral Res. 24, 59-67;Hostetler, K. Y., Richman, D. D., Sridhar, C. N. Felgner, P. L, Felgner,J., Ricci, J., Gardener, M. F. Selleseth, D. W. and Ellis, M. N. (1994b)Phosphatidylazidothymidine and phosphatidyl-ddC: Assessment of uptake inmouse lymphoid tissues and antiviral activities in humanimmunodeficiency virus-infected cells and in rauscher leukemiavirus-infected mice. Antimicrobial Agents Chemother. 38,2792-2797;Hunston, R. N., Jones, A. A. McGuigan, C., Walker, R. T., Balzarini, J.,and De Clercq, E. (1984) Synthesis and biological properties of somecyclic phosphotriesters derived from 2′-deoxy-5-fluorouridine. J. Med.Chem. 27, 440-444; Ji, Y. H., Moog, C., Schmitt, G., Bischoff, P. andLuu, B. (1990); Monophosphoric acid diesters of 7b-hydroxycholesteroland of pyrimidine nucleosides as potential antitumor agents: synthesisand preliminary evaluation of antitumor activity. J. Med. Chem. 33,2264-2270; Jones, A. S., McGuigan, C., Walker, R. T., Balzarini, J. andDeClercq, E. (1984) Synthesis, properties, and biological activity ofsome nucleoside cyclic phosphoramidates. J. Chem. Soc. Perkin Trans. I,1471-1474; Juodka, B. A. and Smart, J. (1974) Synthesis ofditribonucleoside a(P→N) amino acid derivatives. Coll. Czech. Chem.Comm. 39, 363-968; Kataoka, S., Imai, J., Yamaji, N., Kato, M., Saito,M., Kawada, T. and Imai, S. (1989) Alkylated cAMP derivatives; selectivesynthesis and biological activities. Nucleic Acids Res. Sym. Ser., 21,1-2; Kataoka, S., Uchida, R. and Yamaji, N. (1991) A convenientsynthesis of adenosine 3′,5′ cyclic phosphate (cAMP) benzyl and methyltriesters. Heterocycles 32, 1351-1356; Kinchington, D., Harvey, J. J.,O'Connor, T. J., Jones, B. C. N. M., Devine, K. G., Taylor-Robinson, D.,Jeffries, D. J. and McGuigan, C. (1992) Comparison of antiviral effectsof zidovudine phosphoramidate and phosphorodiamnidate derivativesagainst HIV and ULV in vitro. Antiviral Chem. Chemother. 3, 107-112;Kodama, K., Morozumi, M., Saitoh, K. I., Kuninaka, H., Yoshino, H. andSaneyoshi, M. (1989) Antitumor activity and pharmacology of1-b-D-arabinofiuranosylcytosine-5′-stearylpbosphate; an orally activederivative of 1-b-D-arabinofuranosylcytosine. Jpn. J. Cancer Res. 80,679-685; Korty, M. and Engels, J. (1979) The effects of adenosine- andguanosine 3′,5′-phosphoric and acid benzyl esters on guinea-pigventricular myocardium. Naunyn-Schmiedeberg's Arch. Pharmacol. 310,103-111; Kumar, A., Goe, P. L., Jones, A. S. Walker, R. T. Balzarini, J.and De Clercq, E. (1990) Synthesis and biological evaluation of somecyclic phosphoramidate nucleoside derivatives. J. Med. Chem. 33,2368-2375; LeBec, C., and Huynh-Dinh, T. (1991) Synthesis of lipophilicphosphate triester derivatives of 5-fluorouridine and arabinocytidine asanticancer prodrugs. Tetrahedron Lett. 32,6553-6556; Lichtenstein, J.,Barner, H. D. and Cohen, S. S. (1960) The metabolism of exogenouslysupplied nucleotides by Escherichia coli., J. Biol. Chem. 235, 457-465;Lucthy, J., Von Daeniken, A., Friederich, J. Manthey, B., Zweifel, J.,Schlatter, C. and Benn, M. H. (1981) Synthesis and toxicologicalproperties of three naturally occurring cyanoepithioalkanes. Mitt. Geg.Lebensmittelunters. Hyg. 72, 131-133 (Chem. Abstr. 95, 127093);McGuigan, C. Tollerfield, S. M. and Riley, P. A. (1989) Synthesis andbiological evaluation of some phosphate triester derivatives of theanti-viral drug Ara. Nucleic Acids Res. 17, 6065-6075; McGuigan, C.,Devine, K. G., O'Connor, T. J., Galpin, S. A., Jeffries, D. J. andKinchington, D. (1990a) Synthesis and evaluation of some novelphosphoramidate derivatives of 3′-azido-3′-deoxythymidine (AZT) asanti-HIV compounds. Antiviral Chem. Chemother. 1, 107-113; McGuigan, C.,O'Connor, T. J., Nicholls, S. R. Nickson, C. and Kinchington, D. (1990b)Synthesis and anti-HIV activity of some novel substituted dialkylphosphate derivatives of AZT and ddCyd. Antiviral Chem. Chemother. 1,355-360; McGuigan, C., Nicholls, S. R., O'Connor, T. J., andKinchington, D. (1990c) Synthesis of some novel dialkyl phosphatederivative of 3′-modified nucleosides as potential anti-AIDS drugs.Antiviral Chem. Chemother. 1, 25-33; McGuigan, C., Devine, K. G.,O'Connor, T. J., and Kinchington, D.(1991) Synthesis and anti-HIVactivity of some haloalkyl phosphoramidate derivatives of3′-azido-3′-deoxythymidine (AZT); potent activity of the trichloroethylmethoxyalaninyl compound. Antiviral Res. 15, 255-263; McGuigan, C.,Pathirana, R. N., Mahmood, N., Devine, K. G. and Hay, A. J. (1992) Arylphosphate derivatives of AZT retain activity against HIV-1 in cell lineswhich are resistant to the action of AZT. Antiviral Res. 17, 311-321;McGuigan, C., Pathirana, R. N., Choi, S. M., Kinchington, D. andO'Connor, T. J. (1993a) Phosphoramidate derivatives of AZT as inhibitorsof HIV; studies on the carboxyl terminus. Antiviral Chem. Chemother. 4,97-101; McGuigan, C., Pathirana, R. N., Balzarini, J. and De Clercq, E.(1993b) intracellular delivery of bioactive AZT nucleotides by arylphosphate derivatives of AZT. J. Med. Chem. 36, 1048-1052.

[0053] The L-(2′ or 3′-A-5-FddC nucleoside in another embodiment can beprovided as a 5′ ether lipid or a 5′-phospholipid ether, as disclosed inthe following references, which are incorporated by reference herein:Kucera, L. S., N. Lyer, E. Leake, A. Raben, Modest E. J., D. L. W., andC. Piantadosi. 1990. Novel membrane-interactive ether lipid analogs thatinhibit infectious HIV-1 production and induce defective virusformation. AIDS Res Hum Retroviruses. 6:491-501; Piantadosi, C., J.Marasco C. J., S. L. morris-Natschke, K. L. Meyer, F. Gumus, J. R.Surles, K. S. lshaq, L. S. Kucera, N. lyer, C. A. Wallen, S. Piantadosi,and E. J. Modest. 1991-Synthesis and evaluation of novel ether lipidnucleoside conjugates for anti-HIV activity. J Med Chem. 34:1408-1414;Hostetler, K. Y., D. D. Richman, D. A. Carson, L. M. Stuhmiller, G. M.T. van Wijk, and H. van den Bosch. 1992. Greatly enhanced inhibition ofhuman immunodeficiency virus type 1 replication in CEM and HT4-6C cellsby 31-deoxythymidine diphosphate dimyristoylglycerol, a lipid prodrug of31-deoxythymidine. Antimicrob Agents Chemother. 36:2025-2029; Hostetler,K. Y., L. M. Stuhmiller, H. B. Lenting, H. van den Bosch, and D. D.Richman. 1990. Synthesis and antiretroviral activity of phospholipidanalogs of azidothymidine and other antiviral nucleosides. J. Biol Chem.265:6112-7.

[0054] The question of chair-twist equilibria for the phosphate rings ofnucleoside cyclic 3′,5′-monophosphates. ¹HNMR and x-ray crystallographicstudy of the diasteromers of thymidine phenyl cyclic3′,5′-monophosphate. J. Am. Chem. Soc. 109,4058-4064; Nerbonne, J. M.,Richard, S., Nargeot, J. and Lester, H. A. (1984) New photoactivatablecyclic nucleotides produce intracellular jumps in cyclic AMP and cyclicGMP concentrations. Nature 301, 74-76; Neumann, J. M., Hervé, M.,Debouzy, J. C., Guerra, F. I., Gouyette, C., Dupraz, B. and Huynh-Dinh,T. (1989) Synthesis and transmembrane transport studies by NMR of aglucosyl phospholipid of thymidine. J. Am. Chem. Soc. 111, 4270-4277;Ohno, R., Tatsumi, N., Hirano, M., Imai, K. Mizoguchi, H., Nakamura, T.,Kosaka, M., Takatuski, K., Yamaya, T., Toyama, K., Yoshida, T., Masaoka,T., Hashimoto, S., Ohshima, T., Kimura, I., Yamada, K. and Kimura, J.(1991) Treatment of myelodysplastic syndromes with orally administered1-b-D-rabinofuranosylcytosine-5′-stearylphosphate. Oncology 48, 451-455.Palomino, E., Kessle, D. and Horwitz, J. P. (1989) A dihydropyridinecarrier system for sustained delivery of 2′,3′-dideoxynucleosides to thebrain. J. Med. Chem. 32, 622-625; Perkins, R. M., Barney, S., Wittrock,R., Clark, P. H., Levin, R. Lambert, D. M., Petteway, S. R.,Serafinowska, H. T., Bailey, S. M., Jackson, S., Hamden, M. R. Ashton,R., Sutton, D., Harvey, J. J. and Brown, A. G. (1993) Activity ofBRL47923 and its oral prodrug, SB203657A against a rauscher murineleukemia virus infection in mice. Antiviral Res. 20 (Suppl. I). 84;Piantadosi, C., Marasco, C. J., Jr., Morris-Natschke, S. L., Meyer, K.L., Gumus, F., Surles, J. R., Ishaq, K. S., Kucera, L. S. Iyer, N.,Wallen, C. A., Piantadosi, S. and Modest, E. J. (1991) Synthesis andevaluation of novel ether lipid nucleoside conjugates for anti-HIV-1activity. J. Med. Chem. 34, 1408-1414; Pompon, A., Lefebvre, I., Imbach,J. L., Kahn, S. and Farquhar, D. (1994) Decomposition pathways of themono- and bis(pivaloyloxymethyl) esters ofazidothymidine-5′-monophosphate in cell extract and in tissue culturemedium; an application of the ‘on-line ISRP-cleaning’ HPLC technique.Antiviral Chem. Chemother. 5, 91-98; Postemark, T. (1974) Cyclic AMP andcyclic GMP. Annu. Rev. Pharmacol. 14, 23-33; Prisbe, E. J., Martin, J.C. M., McGee, D. P. C., Barker, M. F., Smee, D. F. Duke, A. E.,Matthews, T. R. and Verheyden, J. P. J. (1986) Synthesis and antiherpesvirus activity of phosphate and phosphonate derivatives of9-[(1,3-dihydroxy-2-propoxy)methyl] guanine. J. Med. Chem. 29, 671-675;Pucch, F., Gosselin, G., Lefebvre, I., Pompon, A., Aubertin, A. M. Dim,A. and Imbach, J. L. (1993) Intracellular delivery of nucleosidemonophosphate through a reductase-mediated activation process. AntiviralRes. 22, 155-174; Pugaeva, V. P., Klochkeva, S. I., Mashbits, F. D. andEizengart, R. S. (1969). Toxicological assessment and health standardratings for ethylene sulfide in the industrial atmosphere. Gig. Trf.Prof. Zabol. 13, 47-48 (Chem. Abstr. 72, 212); Robins, R. K. (1984) Thepotential of nucleotide analogs as inhibitors of retroviruses andtumors. Pharm. Res. 11-18; Rosowsky, A., Kim. S. H., Ross and J. Wick,M. M. (1982) Lipophilic 5′-(alkylphosphate) esters of1-b-D-arabinofuranosylcytosine and its N⁴-acyl and 2.2′-anhydro-3′0-acylderivatives as potential prodrugs. J. Med. Chem. 25, 171-178; Ross, W.(1961) Increased sensitivity of the walker turnout towards aromaticnitrogen mustards carrying basic side chains following glucosepretreatment. Biochem. Pharm. 8, 235-240; Ryu, E. K., Ross, R. J.Matsushita, T., MacCoss, M., Hong, C. I. and West, C. R. (1982).Phospholipid-nucleoside conjugates. 3. Synthesis and preliminarybiological evaluation of 1-b-D-arabinofuiranosylcytosine5′-diphosphate[-], 2-diacylglycerols. J. Med. Chem. 25, 1322-1329;Saffhill, R. and Hume, W. J. (1986) The degradation of5-iododeoxyuridine and 5-bromodeoxyuridine by serum from differentsources and its consequences for the use of these compounds forincorporation into DNA. Chem. Biol. Interact. 57, 347-355; Saneyoshi,M., Morozumi, M., Kodama, K., Machida, J., Kuninaka, A. and Yoshino, H.(1980) Synthetic nucleosides and nucleotides. XVI. Synthesis andbiological evaluations of a series of 1-b-D-arabinofuranosylcytosine5′-alkyl or arylphosphates. Chem. Pharm. Bull. 28, 2915-2923; Sastry, J.K., Nehete, P. N., Khan, S., Nowak, B. J., Plunkett, W., Arlinghaus, R.B. and Farquhar, D. (1992) Membrane-permeable dideoxyuridine5′-monophosphate analogue inhibits human immunodeficiency virusinfection. Mol. Pharmacol. 41, 441-445; Shaw, J. P., Jones, R. J.Arimilli, M. N., Louie, M. S., Lee, W. A. and Cundy, K. C. (1994) Oralbioavailability of PMEA from PMEA prodrugs in male Sprague-Dawley rats.9th Annual AAPS Meeting. San Diego, Calif. (Abstract). Shuto, S., Ueda,S., Imamura, S., Fukukawa, K. Matsuda, A. and Ueda, T. (1987) A facileone-step synthesis of 5′-phosphatidylnucleosides by an enzymatictwo-phase reaction. Tetrahedron Lett. 28, 199-202; Shuto, S., Itoh, H.,Ueda, S., Imamura, S., Kukukawa, K., Tsujino, M., Matsuda, A. and Ueda,T. (1988) A facile enzymatic synthesis of5′-(3-sn-phosphatidyl)nucleosides and their antileukemic activities.Chem. Pharm. Bull. 36, 209-217. One preferred phosphate prodrug group isthe S-acyl-2-thioethyl group, also referred to as “SATE.”

[0055] A general process for the stereospecific synthesis of3′-substituted β-L-dideoxynucleosides is shown in FIG. 1. A generalprocess for the stereospecific synthesis of 2′-substitutedβ-L-dideoxynucleosides is shown in FIG. 2. A detailed synthesis ofβ-L-(3′-azido)-2′,3′-dideoxy-5-fluorocytosine is provided in FIG. 3 andin Example 1 below. A detailed synthesis ofβ-L-(2′-azido)-2′,3′-dideoxy-5-fluorocytosine is provided in FIG. 4 andin Example 2 below.

EXAMPLE 1 Preparation of β-L-(3′-azido)-2′,3′-dideoxy-5-fluorocytosine

[0056] Melting points were determined in open capillary tubes on aGallenkamp MFB-595-010 M apparatus and are uncorrected. The UVabsorption spectra were recorded on an Uvikon 931 (KONTRON)spectrophotometer in ethanol. ¹H—NMR spectra were run at roomtemperature in DMSO-d₆ with a Bruker AC 250 or 400 spectrometer.Chemical shifts are given in ppm, DMSO-d₅ being set at 2.49 ppm asreference. Deuterium exchange, decoupling experiments or 2D-COSY wereperformed in order to confirm proton assignments. Signal multiplicitiesare represented by s (singlet), d (doublet), dd (doublet of doublets), t(triplet), q (quadruplet), br (broad), m (multiplet). All J-values arein Hz. FAB mass spectra were recorded in the positive-(FAB>0) ornegative (FAB<0) ion mode on a JEOL DX 300 mass spectrometer. The matrixwas 3-nitrobenzyl alcohol (NBA) or a mixture (50:50, v/v) of glyceroland thioglycerol (GT). Specific rotations were measured on aPerkin-Elmer 241 spectropolarimeter (path length 1 cm) and are given inunits of 10⁻¹ deg cm² g⁻¹. Elemental analysis were carried out by the“Service de Microanalyses du CNRS, Division de Vernaison” (France).Analyses indicated by the symbols of the elements or functions werewithin±0.4% of theoretical values. Thin layer chromatography wasperformed on precoated aluminium sheets of Silica Gel 60 F₂₅₄ (Merck,Art. 5554), visualization of products being accomplished by UVabsorbency followed by charring with 10% ethanolic sulfuric acid andheating. Column chromatography was carried out on Silica Gel 60 (Merck,Art. 9385) at atmospheric pressure.

[0057] 1-(2-O-Acetyl-3,5-di-O-Benzoyl-β-L-Xylofuranosyl)-5-Fluorouracil(2)

[0058] A suspension of 5-fluorouracil (5.0 g, 38.4 mmol) was treatedwith hexamethyldisilazane (HMDS, 260 mL) and a catalytic amount ofammonium sulfate during 18 h under reflux. After cooling to roomtemperature, the mixture was evaporated under reduced pressure, and theresidue obtained as a colorless oil was diluted with anhydrous1,2-dichloroethane (260 mL). To the resulting solution was added1,2-di-ο-acetyl-3,5-di-ο-benzoyl-L-xylofuranose 1 (11.3 g, 25.6 mmol)[Ref.: Gosselin, G.; Bergogne, M.-C.; Imbach, J.-L., “Synthesis andAntiviral Evaluation of β-L-Xylofuranosyl Nucleosides of the FiveNaturally Occurring Nucleic Acid Bases”, Journal of HeterocyclicChemistry, 1993, 30 (October-November), 1229-1233] in anhydrous1,2-dichloroethane (130 mL), followed by addition of trimethylsilyltrifluoromethanesulfonate (TMSTf, 9.3 mL, 51.15 mmol). The solution wasstirred for 6 h at room temperature under argon atmosphere, then dilutedwith chloroform (1 L), washed with the same volume of a saturatedaqueous sodium hydrogen carbonate solution and finally with water (2×800mL). The organic phase was dried over sodium sulphate, then evaporatedunder reduced pressure. The resulting crude material was purified bysilica gel column chromatography [eluent: stepwise gradient of methanol(0-4%) in methylene chloride] to give 2 (11.0 g, 84% yield) as a whitefoam; mp=96-98° C.; UV (ethanol): λ_(max)=228 nm (ε=25900) 266 nm(ε=9000), λ_(min)=250 nm (ε=7200); ¹H—NMR (DMSO-d₆): δ 11.1 (br s, 1H,NH), 8.05 (1H, H-6, J_(6-F5)=6.8 Hz), 7.9-7.4 (m, 10H, 2 C₆H₅CO), 5.99(d, 1H, H-1′, J_(1′-2′)=3.1 Hz), 5.74 (dd, 1H, H-3′, J_(3′-2′)=4.2 Hzand J_(3′-4′)=2.3 Hz), 5.54 (t, 1H, H-2′, J_(2′-1′)=J_(2′-3′)=2,9 Hz),4.8-4.6 (m, 3H, H-4′, H-5′ and H-5″); MS: FAB>0 (matrix GT) m/z 513(M+H)⁺, 383 (S)⁺, 105 (C₆H₅CO)⁺; FAB<0 (matrix GT) m/z 511 (M−H)⁻, 469(M-CH₃CO)⁻, 129 (B)⁻, 121 (C₆H₅CO₂)⁻; [α]_(D) ²⁰=−91 (c, 0.88 DMSO);Anal C₂₅H₂₁FN₂O₉ (C,H, N, F).

[0059] Hydrazine hydrate (2.80 mL, 57.4 mmol) was added to a solution of1-(2-ο-acetyl-3,5-di-ο-benzoyl-β-L-xylofuranosyl)-5-fluorouracil 2 (9.80g, 19.1 mmol) in acetic acid (35 mL) and pyridine (150 mL). Theresulting solution was stirred overnight at room temperature. Acetone(50 mL) was added and the mixture was stirred during 2 h. The reactionmixture was concentrated to a small volume and partitioned between ethylacetate (200 mL) and water (200 mL). Layers were separated and theorganic phase was washed with a saturated aqueous sodium hydrogencarbonate solution (2×200 mL), and finally with water (2×200 mL). Theorganic phase was dried over sodium sulphate, then evaporated underreduced pressure. The resulting residue was purified by silica gelcolumn chromatography [eluent: stepwise gradient of methanol (0-5%) inmethylene chloride] to give pure 3 (7.82 g, 87%), which was crystallizedfrom methylene chloride; mp=93-97° C.; UV (ethanol): λ_(max)=227 nm(ε=22800) 267 nm (ε=8200), λ_(min)=249 nm (ε=5900); ¹H—NMR (DMSO-d₆):δ11.9 (br s, 1H, NH), 8.06 (d, 1H, H-6, J_(6-F5)=6.9 Hz), 8.0-7.4 (m,10H, 2 C₆H₅CO), 6.35 (d, 1H, OH-2′, J_(OH-2′)=3.8 Hz), 5.77 (d, 1H,H-1′, J_(1′-2′)=3.3 Hz), 5.43 (dd, 1H, H-3′, J_(3′-2′)=3.1 Hz andJ_(3′-4′)=1.9 Hz) 4.8-4.6 (m, 3H, H-4′, H-5′ and H-5″), 4.43 (t, 1HH-2′, J=2.3 Hz); MS: FAB>0 (matrix GT) m/z 941 (2M+H)⁺, 471 (M+H)⁺, 341(S)⁺, 131 (BH₂)⁺, 105 (C₆H₅CO)⁺; FAB<0 (matrix GT) m/z 939 (2M−H)⁻, 469(M−H)⁻, 129 (B)⁻, 121 (C₆H₅CO₂); [α]_(D) ²⁰=−110 (c, 1.55 DMSO).

[0060] To a solution of1-(3,5-di-ο-benzoyl-β-L-xylofuranosyl)-5-fluorouracil 3 (15.4 g, 32.7mmol) in anhydrous acetonitrile (650 mL) were added ο-phenylchlorothionoformate (6.80 mL, 49.1 mmol) and 4-dimethylaminopyridine(DMAP, 12.0 g, 98.2 mmol). The resulting solution was stirred at roomtemperature under argon during 1 h and then evaporated under reducedpressure. The residue was dissolved in methylene chloride (350 mL) andthe organic solution was successively washed with water (2×250 mL), withan ice-cold 0.5 N hydrochloric acid (250 mL) and with water (2×250 mL),dried over sodium sulphate and evaporated under reduced pressure. Thecrude material 4 was co-evaporated several times with anhydrous dioxaneand dissolved in this solvent (265 mL). To the resulting solution wereadded under argon tris(trimethylsilyl)silane hydride (12,1 mL, 39.3mmol) and α,α′-azoisobutyronitrile (AIBN, 1.74 g, 10.8 mmol). Thereaction mixture was heated and stirred at 100° C. for 2.5 h underargon, then cooled to room temperature and evaporated under reducedpressure. The residue was purified by silica gel column chromatography[eluent: stepwise gradient of methanol (0-2%) in chloroform] to givepure 5 (13.0 g, 87%), which was crystallized from a diethylether/methanol mixture; mp=182-184° C.; UV (ethanol): λ_(max)=229 nm(ε=25800), 269 nm (ε=9300), λ_(min)=251 nm (ε=6500); ¹H—NMR (DMSO-d₆): δ11.8 (br s, 1H, NH), 8.05 (d, 1H, H-6, J_(6-F5)=7.0 Hz), 8.0-7.4 (m,10H, 2 C₆H₅CO), 6.15 (d, 1H, H-1′, J_(1′-2′)=7.4 Hz), 5.68 (t, 1H, H-3′,J_(3′-2′)=J_(3′-4′)=4.2 Hz), 4.8-4.6 (m, 2H, H-5′ and H″-5),4.6 (m, 1H,H-4′), 3.0-2.8 (m, 1H, H-2′), 2.5-2.3 (d, 1H, H-2″, J=14.8 Hz); MS:FAB>0 (matrix GT) m/z 455 (M+H)⁺, 325 (S)⁺, 131 (BH₂)⁺, 105 (C₆H₅CO)⁺;FAB<0 (matrix GT) m/z 452 (M−H)⁻, 129 (B)⁻; [α]_(D) ²⁰=−125 (c 1.05DMSO); Anal C₂₃H₁₉FN₂O₇ (C, H, N, F).

[0061] Lawesson's reagent (3.1 g, 7.70 mmol) was added under argon to asolution of 5 (5.0 g, 11.0 mmol) in anhydrous 1,2-dichloroethane (200mL) and the reaction mixture was stirred overnight under reflux. Thesolvent was then evaporated under reduced pressure and the residue waspurified by silica gel column chromatography [eluent: stepwise gradientof methanol (0-2%) in chloroform] to give the 4-thio intermediate 6 (80%yield) as a yellow foam; mp=178-179° C.; UV (ethanol): λ_(max)=230 nm(ε=24900), 273 nm (ε=6900), 333 nm (ε=19200), λ_(min)=258 nm (ε=5900),289 nm (ε=5300); ¹H—NMR (DMSO-d₆): δ 13.1 (br s, 1H, NH), 8.10 (d, 1H,H-6, J_(6-F5)=4,6 Hz), 8.1-7.4 (m, 10H, 2 C₆H₅CO), 6.09 (d, 1H, H-1′,J_(1′-2′)=7.3 Hz), 5.68 (t, 1H, H-3′, J_(3′-2′) =J _(3′-4′)=4.1 Hz),4.9-4.8 (m, 2H, H-5′ and H-5″), 4.7 (m, 1H, H-4′), 2.9 (m, 1H, H-2′),2.5 (m, 1H, H-2″); MS: FAB>0 (matrix GT) m/z 941 (2M+H)⁺, 471 (M+H)⁺,325 (S)⁺, 147 (BH₂)⁺, 105 (C₆H₅CO)⁺; FAB<0 (matrix GT) m/z 469 (M−H)⁻,145 (B)⁻, 121 (C₆H₅CO₂)⁻; [α]_(D) ²⁰=−271 (c, 0,90 DMSO); AnalC₂₃H₁₉FN₂O₆S (C, H, N, F).

[0062] A solution of this 4-thio intermediate 6 (1.0 g, 2.13 mmol) inmethanolic ammonia (previously saturated at −10° C. and tightly stopped)(60 mL) was heated at 100° C. in a stainless-steel bomb for 3 h and thencooled to 0° C. The solution was evaporated to dryness under reducedpressure and the residue co-evaporated several times with methanol. Thecrude material was dissolved in water and the resulting solution waswashed four times with methylene chloride. The aqueous layer wasevaporated under reduced pressure and the residue was purified by silicagel column chromatography [eluent: stepwise gradient of methanol (3-20%)in methylene chloride]. Finally, the appropriate fractions wereevaporated under reduced pressure, diluted with methanol and filteredthrough a unit Millex HV-4 (0,45 μm, Millipore) to provide 0.44 g of 7(84% yield) which was crystallized from an ethyl acetate/methanolmixture; mp=199-201° C.; UV (ethanol): λ_(max)=226 nm (ε=7700), 281 nm(ε=8500), λ_(min)=262 nm (ε=6300); ¹H—NMR (DMSO-d₆): δ 7.99 (d, 1H, H-6,J_(6-F5)=7.4 Hz), 7.7-7.4 (br d, 2H, NH₂), 5.98 (d, 1H, H-1′,J_(1′-2′)=8.1 Hz), 5.25 (d, 1H, OH-3′, J_(OH-3′)=3.4 Hz), 4.71 (t, 1H,OH-5′, J_(OH-5′)=J_(OH-5″)=5.6 Hz), 4.2 (m, 1H, H-3′), 3.8-3.6 (m, 3H,H-4′, H-5′ and H-5″), 2.5 (m, 1H, H-2′), 1.8 (m, 1H, H-2″); MS: FAB>0(matrix GT) m/z 491 (2M+H)⁺, 246 (M+H)⁺, 130 (BH₂)⁺; FAB<0 (matrix GT)m/z 489 (2M−H)⁻, 244 (M−H)⁻, 128 (B)⁻; [α]_(D) ²⁰=−21 (c, 0.92 DMSO);Anal C₉H₁₂FN₃O₄ (C, H, N, F).

[0063] To a solution of 7 (1.69 g, 6.89 mmol) in dry pyridine (35 mL)was added dropwise under argon atmosphere t-butyldimethylsilyl chloride(1.35 g, 8.96 mmol) and the mixture was stirred for 5 h at roomtemperature. Then the mixture was poured onto a saturated aqueous sodiumhydrogen carbonate solution (100 mL) and extracted with chloroform(3×150 mL). Combined extracts were washed with water (2×200 mL) and thendried over sodium sulphate and evaporated under reduced pressure. Theresidue was purified by silica gel column chromatography [eluent:stepwise gradient. of methanol (2-10%) in methylene chloride] to givepure 8 (2.94 g, 87%), as a white solid: mp 177-179° C.; UV (ethanol):λ_(max) 241 nm (ε 9900), 282 nm (ε 10000), λ_(min) 226 nm (ε 8200), 263nm (ε 7600); ¹H NMR (DMSO-d₆): δ 7.95 (d, 1H, H-6, J_(6-F5)=7.3 Hz),7.8-7.3 (br d, 2h, NH₂), 6.00 (dd, 1H, H-1′, J_(1′-2′)=6.1 Hz andJ_(1′-2″)=1.9 Hz), 5.3 (br s, 1H, OH-3′), 4.2 (br s, 1H, H-3′), 3.9-3.7(m, 3H, H-4′, H-5′ and H-5″), 2.5 (m, 1H, H-2′), 1.81 (br d, 1H, H-2″,J=14.6 Hz), 0.86 (s, 9H, (CH₃)₃C—Si), 0.05 (s, 6H, (CH₃)₂Si); MS (matrixGT): FAB>0 m/z 719 (2M+H)⁺, 360 (M+H)⁺, 130 (BH₂)⁺, 115 (TBDMS)⁺; FAB<0m/z 717 (2M−H)⁻, 358 (M−H)⁻, 128 (B)⁻; [α]_(D) ²⁰=−23 (c, 0.96 DMSO).

[0064] A suspension of 8 (0.70 g, 1.96 mmol) in dry pyridine (30 mL) wasstirred under argon and cooled to 0° C. Methanesulfonyl chloride (MsCl,0.46 mL, 5.88 mmol) was added dropwise and the reaction mixture stirredat 0° C. for 5 h. Then the mixture was poured onto ice/water (100 mL)and extracted with chloroform (3×100 mL). Combined extracts were washedwith a 5% aqueous sodium hydrogen carbonate solution (100 mL), withwater (2×100 mL), dried over sodium sulphate and evaporated underreduced pressure. The resulting residue was purified by silica gelcolumn chromatography [eluent: stepwise gradient of methanol (8-12%) intoluene] to give pure 9 (0.56 g, 65%) as a white solid: mp 83-84° C.; UV(ethanol): λ_(max) 242 nm (ε 8500), 282 nm (ε 8800), λ_(min) 225 nm (ε6400), 264 nm (ε 6300); ¹H NMR (DMSO-d₆): δ 7.8-7.3 (br d, 2H, NH₂),7.60 (d, 1H, H-6, J_(6-F5)=7.0 Hz), 5.93 (dd, 1H, H-1′, J_(1′-2′)=4.5 Hzand J_(1′-2″)=2.0 Hz), 5.2 (m, 1H, H-3′), 4.1 (m, 1H, H-4′), 3.9-3.7 (m,2H, H-5′ and H-5″), 3.17 (s, 3H, CH₃SO₂), 2.7 (m, 1H, H-2′), 2.1 (m, 1H,H-2″), 0.99 (s, 9H, (CH₃)₃C—Si), 0.05 (s, 6H, (CH₃)₂Si); MS (matrix GT):FAB>0 m/z 875 (2M+H)⁺, 438 (M+H)⁺, 342 (M-CH₃SO₃)⁺, 130 (BH₂)⁺; FAB<0m/z 873 (2M−H)⁻, 436 (M−H)⁻, 128 (B)⁻, 95 (CH₃SO₃)⁻; [α]_(D) ²⁰=−28 (c,0.96 DMSO).

[0065] To a solution of 9 (520 mg, 1.19 mmol) in anhydrousdimethylformamide (12 mL) was added lithium azide moistened with 10%methanol (300 mg, 5.31 mmol). The reaction mixture was stirred at 100°C. during 2.5 h, and then cooled to room temperature, poured ontoice/water (200 mL) and extracted with chloroform (3×100 mL). Combinedextracts were washed with saturated aqueous sodium hydrogen carbonatesolution (2×100 mL), with water (5×100 mL), and then dried over sodiumsulphate and evaporated under reduced pressure. The residue was purifiedby silica gel column chromatography [eluent : methanol (4%) inchloroform] to give pure 10 (327 mg, 72%), which was crystallized from adiethyl ether/methanol mixture: mp 146-147° C.; UV (ethanol): λ_(max)243 nm (ε 8700), 283 nm (ε8400), λ_(min) 226 nm (ε 7200), 264 nm (ε6700); ¹H NMR (DMSO-d₆): δ 7.90 (d, 1H, H-6, J_(6-F5)=7.0 Hz), 7.8-7.5(br d, 2H, NH₂), 6.0 (m, 1H, H-1′), 4.3 (m, 1H, H-3′), 3.9-3.7 (m, 3H,H-4′, H-5′ and H″-5), 2.4-2.2 (m, 2H, H-2′ and H-2″), 0.87 (s, 9H,(CH₃)₃C—Si), 0.05 (s, 6H, (CH₃)₂Si); MS (matrix GT): FAB>0 m/z 769(2M+H)⁺, 385 (M+H)⁺, 130 (BH₂)⁺; FAB<0 m/z 383 (M−H)⁻; [α]_(D) ²⁰=−67(c, 0.96 DMSO).

[0066] A 1 M solution of tetrabutylammonium trifluoride intetrahydrofurane (TBAF/THF, 1.53 mL, 1.53 mmol) was added to a solutionof 10 (295 mg, 0.67 mmol) in anhydrous THF (4 mL). The resulting mixturewas stirred at room temperature for 1.5 h and evaporated under reducedpressure. The residue was purified by silica gel column chromatography[eluent: stepwise gradient of methanol (4-8%) in chloroform]. Finally,the appropriate fractions were evaporated under reduced pressure,diluted with methanol and filtered through a unit Millex HV-4 (0,45 μm,Millipore) to give pure 11 (199 mg, 96%), which was crystallized fromethanol: mp 188-189° C. (lit.: mp 164-166° C. for the D-enantiomer); UV(ethanol): λmax 243 nm (ε 8700), 283 nm (ε 8100), λmin 226 nm (ε 7100),264 nm (ε 6500); ¹H NMR (DMSO-d₆): δ 8.08 (d, 1H, H-6, J_(6-F5)=7.3 Hz),7.8-7.5 (br d, 2H, NH₂), 6.0 (m, 1H, H-1′), 5.3 (br s, 1H, OH-5′), 4.4(m, 1H, H-3′), 3.8 (m, 1H, H-4′), 3.7-3.5 (m, 2H, H-5′ and H-5″), 2.3(m, 2H, H-2′ and H-2″); MS (matrix GT): FAB>0 m/z 811 (3M+H)⁺, 725(2M+2G+H)⁺, 633 (2M+G+H)⁺, 541 (2M+H)⁺, 363 (M+G+H)⁺, 271 (M+H)⁺, 142(S)⁺, 130 (BH₂)⁺; FAB<0m/z 647 (2M+T−H)⁻, 539 (2M−H)⁻, 377 (M+T−H)⁻, 269(M−H)⁻, 128 (B)⁻; [α]_(D) ²⁰=−31 (c, 0.90 DMSO); Anal. (C₉H₁₁FN₆O₃) C,H, N, F. Analytical data Anal Calculated Anal Found Compound Formula C HN F C H N F 2 C₂₅H₂₁FN₂O₉ 58.59 4.13 5.47 3.71 58.33 4.25 4.24 3.49 5C₂₃H₁₉FN₂O₇ 60.79 4.21 6.17 4.18 61.22 4.26 6.18 3.90 6 C₂₃H₁₉FN₂O₆S58.71 4.07 5.96 4.04 58.25 4.10 5.91 4.00 7 C₉H₁₂FN₃O₄ 44.08 4.87 17.177.75 43.87 5.13 16.81 7.42 11 C₉H₁₁FN₆O₃ 40.00 4.10 31.10 7.03 40.353.83 31.38 7.12

EXAMPLE 2 Preparation of β-L-(2′-azido)-2′,3′-dideoxy-5-fluorocytosine

[0067] General procedures and instrumentation used have been describedin Example 1 in the Experimental protocols part of the synthesis of the3′ isomer (3′-N₃-β-L-FddC).

[0068] A suspension of 5-fluorouracil (5.15 g, 39.6 mmol) was treatedwith hexamethyldisilazane (HMDS, 257 mL) and a catalytic amount ofammonium sulfate during 18 h under reflux. After cooling to roomtemperature, the mixture was evaporated under reduced pressure, and theresidue obtained as a colourless oil was diluted with anhydrous1,2-dichloroethane (290 mL). To the resulting solution was added1,2-di-ο-acetyl-3-deoxy-5-ο-benzoyl-L-erythro-pentofuranose 12 (8.5 g,26.4 mmol) [Ref.: Mathé, C., Ph.D. Dissertation, Université deMontpellier II-Sciences et Techniques du Languedoc, Montpellier(France), Sep. 13, 1994; Gosselin, G.; Mathé, C.; Bergogne, M.-C.;Aubertin, A. M.; Kim, A.; Sommadossi, J. P.; Schinazi, R. F.; Imbach, J.L., “2′- and/or 3′-deoxy-β-L-pentofuranosyl nucleoside derivatives:stereospecific synthesis and antiviral activities,” Nucleosides &Nucleotides, 1994, 14 (3-5), 611-617] in anhydrous 1,2-dichloroethane(120 mL), followed by addition of trimethylsilyltrifluoromethanesulfonate (TMSTf, 9.6 mL, 52.8 mmol). The solution wasstirred for 5 h at room temperature under argon atmosphere, then dilutedwith chloroform (200 mL), washed with the same volume of a saturatedaqueous sodium hydrogen carbonate solution and finally with water (2×300mL). The organic phase was dried over sodium sulphate, then evaporatedunder reduced pressure. The resulting crude material was purified bysilica gel column chromatography [eluent: stepwise gradient of methanol(0-6%) in methylene chloride] to give pure 13 (8.59 g, 83%), which wascrystallized from toluene: mp 65-68° C.; UV (ethanol): λ_(max) 228 nm (ε11200) 268 nm (ε 14000), λ_(min) 242 nm (ε 7800); ¹H NMR (DMSO-d₆): δ11.9 (br s, 1H, NH), 8.0-7.5 (m, 6H, C₆H₅CO and H-6), 5.8 (m, 1H, H-1′),5.3 (m, 1H, H-2′), 4.6-4.5 (m, 3H, H-4′, H-5′ and H-5″), 2.4-2.3 (m, b1H, H-3′), 2.1-2.0 (m, 4H, H-3″ and CH₃CO); MS (matrix GT): FAB>0 m/z393 (M+H)⁺, 263 (S)⁺, 105 (C₆H₅CO)⁺; FAB<0 m/z 391 (M−H)⁻, 331(M-[CH₃CO₂H]—H)⁻, 129 (B)⁻, 121 (C₆H₅CO₂)⁻; [α]_(D) ²⁰=−8 (c,1.00 DMSO);Anal. (C₁₈H₁₇FN₂O₇; ⅔ C₇H₈) C, H, N, F.

[0069] To a solution of 13 (5.90 g, 15.0 mmol) in tetrahydrofurane (THF,175 mL), was added sodium methoxide (2.84 g, 52.6 mmol). The resultingsuspension was stirred at room temperature during 5 h and thenneutralized by addition of Dowex 50 W X 2 (H⁺ form). The resin wasfiltered and washed with warm methanol, and the combined filtrates wereevaporated to dryness. Column chromatography of the residue on silicagel [eluent: stepwise gradient of methanol (0-8%) in methylene chloride]afforded 14 (4.11 g, 78%), which was crystallized from a methylenechloride/methanol mixture: mp 154-156° C.; UV (ethanol): λ_(max) 226 nm(ε 23000), 268 nm (ε 16000), λ_(min) 246 nm (ε 8900); ¹H NMR (DMSO-d₆):δ 11.8 (br s, 1H, NH), 8.0-7.5 (m, 6H, C₆H₅CO and H-6), 5.6 (br s, 2H,H-1′ and OH-2′), 4.5 (m, 3H, H-4′, H-5′ and H-5″), 4.3 (m, 1H, H-2′),2.1-2.0 (m, 1H, H-3′), 1.9 (m, 1H, H-3″); MS (matrix GT): FAB>0 m/z 701(2M+H)⁺, 351 (M+H)⁺, 221 (S)⁺, 131 (BH₂)⁺, 105 (C₆H₅CO)⁺; FAB<0 m/z 1049(3M−H)⁻, 699 (2M−H)⁻, 441 (M+G−H)⁻, 349 (M−H)⁻, 129 (B)⁻, 121(C₆H₅CO₂)⁻; [α]_(D) ²⁰=−3 (c, 1.04 DMSO); Anal. (C₁₆H₁₅FN₂O₆) C, H, N, F

[0070] Dicyclohexylcarbodiimide (DCC, 3.53 g, 17.1 mmol) anddichloroacetic acid (0.235 mL, 2.56 mmol) were added to a solution of 14(2.00 g, 5.71 mmol) in anhydrous benzene (50 mL), DMSO (35 mL) andpyridine (0.46 mL). The resulting solution was stirred at roomtemperature under argon during 4 h and diluted with ethyl acetate (300mL). Oxalic acid (1.54 g, 17.1 mmol) dissolved in methanol (4.6 mL) wasadded and the reaction mixture was stirred at room temperature during 1h and then filtered to eliminate precipitated dicyclohexylurea (DCU).The filtrate was washed with brine (3×300 mL), with a saturated aqueoussodium hydrogen carbonate solution (2□300 mL) and finally with water(3×200 mL) before being dried over sodium sulphate and evaporated underreduced pressure. The resulting residue was co-evaporated several timeswith absolute ethanol and dissolved in a mixture of absolute ethanol (31mL) and anhydrous benzene (15 mL). The resulting solution was thencooled to 0° C. and sodium borohydride (NaBH_(4,) 0.32 g, 8.56 mmol) wasadded. The reaction mixture was stirred at room temperature under argonduring 1 h and diluted with ethyl acetate (300 mL) filtered. Thefiltrate was washed with a saturated aqueous sodium chloride solution(3×300 mL) and with water (2□200 mL) before being dried over sodiumsulphate and evaporated under reduced pressure. The resulting residuewas purified by silica gel column chromatography [eluent: stepwisegradient of methanol (0-6%) in chloroform] to give pure 15 (1.10 g,55%), as a white foam: mp 171-172□C; UV (ethanol): 80_(max) 228 nm(ε14700) 270 nm (ε 9100), λ_(min) 248 nm (ε 5000); ¹H NMR (DMSO-d₆): δ11.8 (br s, 1H, NH), 8.0-7.5 (m, 6H, C₆H₅CO and H-6), 5.90 (dd, 1H,H-1′, J_(1′-2′)=4.1 Hz and J_(1′-F5)=1.8 Hz), 5,5 (br s, 1H, OH-2′), 4.7(br q, 1H, H-4′, J=11.7 Hz and J=7.0 Hz), 4.4-4.3 (m, 3H, H-2′, H-5′ andH-5″), 2.4 (m, 1H, H-3′), 1.9-1.8 (m, 1H, H-3″); MS (matrix GT): FAB>0m/z 701 (2M+H)⁺, 351 (M+H)⁺, 221 (S)⁺, 131 (BH₂)⁺, 105 (C₆H₅CO)⁺; FAB<0m/z 1049 (3M−H)⁻, 699 (2M−H)⁻, 349 (M−H)⁻, 129 (B)⁻, 121 (C₆H₅CO₂)⁻;[α]_(D) ²⁰=−101 (c, 0.70 DMSO).

[0071] Acetic anhydride (0.88 mL, 9.28 mmol) was added under argon to asolution of 15 (2.50 g, 7.14 mmol) in dry pyridine (50 mL) and theresulting mixture was stirred at room temperature for 22 h. Then,ethanol was added and the solvents were evaporated under reducedpressure. The residue was purified by silica gel column chromatography[eluent: stepwise gradient of methanol (0-2%) in methylene chloride] togive pure 16 (2.69 g, 96%) as a white foam; mp=68-70° C. (foam); UV(ethanol): λ_(max)=239 nm (ε=15000) 267 nm (ε=8800), λ_(min)=248 nm(ε=5600); ¹H NMR (DMSO-d₆): δ ppm 11.9 (br s, 1H, NH), 8.1-7.5 (m, 6H,C₆H₅CO and H-6), 6.10 (d, 1H, H-1′, J_(1′-2′)=4.3 Hz), 5.4 (m, 1H,H-2′), 4.6-4.4 (m, 3H, H-4′, H-5′ and H-5″), 2.6 (m, 1H, H-3′), 2.03 (m,1H, H-3″), 1,86 (s, 3H, CH₃CO); MS (matrix GT): FAB>0 m/z 785 (2M+H)⁺,393 (M+H)⁺, 263 (S)⁺, 131 (BH₂)⁺, 105 (C₆H₅CO)⁺, 43 (CH₃CO)⁺; FAB<0 m/z391 (M−H)⁻, 129 (B)⁻, 121 (C₆H₅CO₂) ⁻, 59 (CH₃CO₂)⁻; [α]_(D) ²⁰=−81 (c,0.95 DMSO).

[0072] Lawesson's reagent (1.9 g, 4.69 mmol) was added under argon to asolution of 16 (2.63 g, 6.70 mmol) in anhydrous 1,2-dichloroethane (165mL) and the reaction mixture was stirred overnight under reflux. Thesolvent was then evaporated under reduced pressure and the residue waspurified by silica gel column chromatography [eluent: stepwise gradientof methanol (0-3%) in methylene chloride] to give the 4-thio derivative17 (2.65 g, 96% yield) as a yellow foam; mp=78-79° C. (foam) ; UV(ethanol): λ_(max)=230 nm (ε=15900) 334 nm (ε=15600), λ_(min)=288 nm(ε=3200); ¹H NMR (DMSO-d₆): δ ppm 13.2 (br s, 1H, NH), 8.1-7.5 (m, 6H,C₆H₅CO and H-6), 6.08 (d, 1H, H-1′, J_(1′-2′)=4.3 Hz), 5.4 (m, 1H,H-2′), 4.7-4.4 (m, 3H, H-4′, H-5′ and H-5″), 2.6 (m, 1H, H-3′), 2.0 (m,1H, H-3″), 1.84 (s, 3H, CH₃CO); MS (matrix GT): FAB>0 m/z 409 (M+H)⁺,263 (S)⁺, 147 (BH₂)⁺, 105 (C₆H₅CO)⁺, 43 (CH₃CO)⁺; FAB<0 m/z 407 (M−H)⁻,145 (B)⁻, 121 (C₆H₅CO₂)⁻, 59 (CH₃CO₂)⁻; [α]_(D) ²⁰=−155 (c, 1.00 DMSO).

[0073] A solution of the 4-thio derivative 17 (0.86 g, 2.19 mmol) inmethanolic ammonia (previously saturated at −10° C. and tightly stopped)(44 mL) was heated at 100° C. in a stainless-steel bomb for 3 h and thencooled to 0° C. The solution was evaporated to dryness under reducedpressure and the residue co-evaporated several times with methanol. Thecrude material was dissolved in water and the resulting solution waswashed four times with methylene chloride. The aqueous layer wasevaporated under reduced pressure and the residue was purified by silicagel column chromatography [eluent: stepwise gradient of methanol (3-12%)in chloroform]. Finally, the appropriate fractions were evaporated underreduced pressure, diluted with methanol and filtered through a unitMillex HV-4 (0.45 μm, Millipore) to provide 0.46 g of 18 (86% yield)which was crystallized from a methylene/methanol mixture; mp=137-138°C.; UV (ethanol): λ_(max)=240 nm (ε=8300) 284 nm (ε=8100), λ_(min)=226nm (ε=7300) 263 nm (ε=5500); ¹H NMR (DMSO-d₆): δ ppm 8.34 (d, 1H, H-6,J_(6-F5)=7.5 Hz), 7.7-7.4 (br pd, 2H, NH₂), 5.83 (dd, 1H, H-1′,J_(1′-2′)=4.4 Hz, J_(1′-F5)=1.9 Hz), 5.22 (d, 1H, OH-2′, J_(OH-2′)=5.1Hz), 5.15 (t, 1H, OH-5′, J_(OH-5′)=J_(OH-5″)=4.8 Hz), 4.3 (m, 1H, H-2′),4.0 (m, 1H, H-4′), 3.6-3.5 (m, 2H, H-5′ and H-5″) 2.2 (m, 1H, H-3′), 1.7(m, 1H, H-3″); MS (matrix GT): FAB>0 m/z 491 (2M+H)⁺, 246 (M+H)⁺, 130(BH₂)⁺; FAB<0 m/z 244 (M−H)⁻, 128 (B)⁻; [α]_(D) ²⁰=−135 (c, 0.89 DMSO).Elemental analysis, C₉H₁₂FN₃O₄, ½ H₂O; Calc. C=42.52; H=5.15; N=16.53;F=7.47; Found: C=43.16; H=5.32; N=16.97; F=6.92.

[0074] To a solution of 18 (1.38 g, 5.63 mmol) in dry pyridine (30 mL)was added dropwise under argon atmosphere t-butyldimethylsilyl chloride(1.10 g, 7.32 mmol) and the mixture was stirred for 10 h at roomtemperature. Then the mixture was poured onto a saturated aqueous sodiumhydrogen carbonate solution (100 mL) and extracted with chloroform(3×150 mL). Combined extracts were washed with water (2×200 mL) and thendried over sodium sulphate and evaporated under reduced pressure. Theresidue was purified by silica gel column chromatography [eluent:stepwise gradient of methanol (2-10%) in methylene chloride] to givepure 19 (1.74 g, 86% yield) as a white solid: mp 202-204° C.; UV(ethanol): λ_(max) 241 nm (ε 7800), 284 nm (ε 7800), λ_(min) 226 nm (ε6600), 263 nm (ε 5400); ¹H NMR (DMSO-d₆): δ 7.77 (d, 1H, H-6,J_(6-F5)=7.1 Hz), 7.7-7.3 (br d, 2H, NH₂), 6.88 (dd, 1H, H-1′,J_(1′-2′)=4.9 Hz and J_(1′-F5)=1.9 Hz), 5.24 (d, 1H, OH-3′,J_(OH-3′)=4.6 Hz), 4.4 (m, 1H, H-2′), 4.0 (m, 1H, H-4′), 3.8-3.7 (m, 2H,H-5′ and H-5″), 2.2 (m, 1H, H-3′), 1.7 (m, 1H, H-3″), 0.84 (s, 9H,(CH₃)₃C—Si), 0.06 (s, 6H, (CH₃)₂Si); MS (matrix GT): FAB>0 m/z 1437(4M+H)⁺, 1078 (3M+H)⁺, 719 (2M+H)⁺, 360 (M+H)⁺, 231 (S)⁺, 130 (BH₂)⁺,115 (TBDMS)⁺; FAB<0 m/z 1076 (3M−H)⁻, 717 (2M−H)⁻, 358 (M−H)⁻, 128 (B)⁻;[60 ]_(D) ²⁰=−107 (c, 0.88 DMSO).

[0075] A suspension of 19 (1.70 g, 4.73 mmol) in dry pyridine (80 mL)was stirred under argon and cooled to 0° C. Methanesulfonyl chloride(MsCl, 1.21 mL, 15.6 mmol) was added dropwise and the reaction mixturestirred at 0° C. for 5 h. Then the mixture was poured onto ice/water(300 mL) and extracted with chloroform (3×300 mL). Combined extractswere washed with a 5% aqueous sodium hydrogen carbonate solution (300mL), with water (2×300 mL) and then dried over sodium sulphate andevaporated under reduced pressure. The resulting residue was purified bysilica gel column chromatography [eluent: stepwise gradient of methanol(8-12%) in toluene] to give pure 20 (1.41 g, 68% yield) as a whitesolid: mp 75-76° C.; UV (ethanol): λ_(max) 243 nm (ε 8100), 282 nm (ε7300), λ_(min) 225 nm (ε 6000), 265 nm (ε 6000); ¹H NMR (DMSO-d₆): δ7.9-7.6 (br d, 2H, NH₂), 7.85 (d, 1H, H-6, J_(6-F5)=7.0 Hz), 6.08 (dd,1H, H-1′, J_(1′-2′)=5.2 Hz and J_(1′-F5)=1.6 Hz), 5.4 (m, 1H, H-2′), 4.1(m, 1H, H-4′), 3.9 (m, 1H, H-5′), 3.7 (m, 1H, H-5″), 3.11 (s, 3H,CH₃SO₂), 2.47 (m, 1H, H-3′), 2.0 (m, 1H, H-2″), 0.85 (s, 9H,(CH₃)₃C—Si), 0.05 (s, 6H, (CH₃)₂Si); MS (matrix GT): FAB>0 m/z 1312(3M+H)⁺, 875 (2M+H)⁺, 438 (M+H)⁺, 309 (S)⁺, 130 (BH₂)⁺; FAB<0 m/z 1310(2M−H)⁻, 873 (2M−H)⁻, 436 (M−H)⁻, 128 (B)⁻, 95 (CH₃SO₃)⁻; [α]_(D) ²⁰=−84(c, 0.84 DMSO).

[0076] To a solution of 20 (442 mg, 1.01 mmol) in anhydrousdilmethylformamide (12 mL) was added lithium azide moistened with 10%methanol (265 mg, 4.87 mmol). The reaction mixture was stirred at 100°C. during 2.5 h, and then cooled to room temperature, poured ontoice/water (200 mL) and extracted with chloroform (3×100 mL). Combinedextracts were washed with a saturated aqueous sodium hydrogen carbonatesolution (2×100 mL), with water (5×100 mL) and then dried over sodiumsulphate and evaporated under reduced pressure. The residue was purifiedby silica gel column chromatography [eluent : methanol (4%) inchloroform] to give pure 21 (291 mg, 75% yield) as a white solid: mp147-148° C.; UV (ethanol): λ_(max) 242 nm (ε 7700), 283 nm (ε 7400),λ_(min) 226 nm (ε 6600), 264 nm (ε 5800); ¹H NMR (DMSO-d₆): δ 8.05 (d,1H, H-6, J_(6-F5)=7.0 Hz), 7.9-7.4 (br d, 2H, NH₂), 5.7 (br s, 1H,H-1′), 4.37 (d, 1H, H-2′, J_(2′-3′)=5.5 Hz), 4.3 (m, 1H, H-4′), 4. (m,1H, H-5′), 3.7 (m, 1H,H-5″), 2.0 (m, 1H, H-3′), 1.8 (m, 1H, H-3″), 0.88(s, 9H, (CH₃)₃C—Si), 0.05 (s, 6H, (CH₃)₂Si); MS (matrix GT): FAB>0 m/z769 (2M+H)⁺, 385 (M+H)⁺, 130 (BH₂)⁺; FAB<0 m/z 1151 (3M−H)⁻, 767(2M−H)⁻, 383 (M−H)⁻, 128 (B)⁻; [α]_(D) ²⁰=+25 (c, 0.95 DMSO).

[0077] A 1 M solution of tetrabutylammonium trifluoride intetrahydrofurane (TBAF/THF, 1.90 mL, 1.90 mmol) was added to a solutionof 21 (480 mg, 1.25 mmol) in anhydrous THF (8 mL). The resulting mixturewas stirred at room temperature for 1.5 h and evaporated under reducedpressure. The residue was purified by silica gel column chromatography[eluent: stepwise gradient of methanol (4-8%) in chloroform]. Finally,the appropriate fractions were evaporated under reduced pressure,diluted with methanol and filtered through a unit Millex HV-4 (0.45 μm,Millipore) to give pure 22 (304 mg, 90% yield), which was crystallizedfrom ethanol: mp 219-221° C.; UV (ethanol): λ_(max) 241 nm (ε 7700), 284nm (ε 7300), λ_(min) 225 nm (ε 6500), 263 nm (ε 5400); ¹H NMR (DMSO-d₆):δ 8.31 (d, 1H, H-6, J_(6-F5)=7.4 Hz), 7.9-7.4 (br d, 2H, NH₂), 5.65 (m,1H, H-1′), 5.32 (br s, 1H, OH-5′), 4.35 (d, 1H, H-2′, J_(2′-3′)=5.6 Hz),4.2 (m, 1H, H-4′), 3.8 (m, 1H, H-5′), 3.6 (m, 1H, H-5″), 2.1 (m, 1H,H-3′), 1.8 (m, 1H, H-2″); MS (matrix GT): FAB>0 m/z 541 (2M+H)⁺, 363(M+G+H)⁺, 271 (M+H)⁺, 130 (BH₂)⁺; FAB<0 m/z 539 (2M−H)⁻, 269 (M−H)⁻, 128(B)⁻; [α]_(D) ²⁰=+29 (c, 0.85 DMSO); Anal. (C₉H₁₁FN₆O₃) C, H, N, F.Analytical data Anal. calculated Anal. found Compd Formula C H N F C H NF 13 C₁₈H₁₇FN₂O₇, ⅔ C₇H₈ 59.99 4.96 6.18 4.19 59.60 4.96 6.02 3.76 14C₁₆H₁₅FN₂O₆ 54.86 4.32 8.00 5.42 54.75 4.16 7.78 5.49 22 C₉H₁₁FN₆O₃40.00 4.10 31.10 7.03 40.07 4.16 31.10 6.99

[0078] Anti-HIV Activity of the Active Compounds

[0079] Antiviral compositions can be screened in vitro for inhibition ofHIV by various experimental techniques. One such technique involvesmeasuring the inhibition of viral replication in human peripheral bloodmononuclear (PBM) cells. The amount of virus produced is determined bymeasuring the quantity of virus-coded reverse transcriptase (RT), anenzyme found in retroviruses, that is present in the cell culturemedium.

[0080] Three-day-old phytohemagglutinin-stimulated PBM cells (10⁶cells/ml) from hepatitis B and HIV-1 seronegative healthy donors wereinfected with HIV-1 (strain LAV) at a concentration of about 100 timesthe 50% tissue culture infectious done (TICD 50) per ml and cultured inthe presence and absence of various concentrations of antiviralcompounds.

[0081] Approximately one hour after infection, the medium, with thecompound to be tested (2 times the final concentration in medium) orwithout compound, was added to the flasks (5 ml; final volume 10 ml).AZT was used as a positive control. The cells were exposed to the virus(about 2×10⁵ dpm/ml, as determined by reverse transcriptase assay ) andthen placed in a CO₂ incubator. HIV-1 (strain LAV) was obtained from theCenters for Disease Control, Atlanta, Ga. The methods used for culturingthe PBM cells, harvesting the virus and determining the reversetranscriptase activity were those described by McDougal et al. (J.Immun. Meth. 76, 171-183, 1985) and Spira et al., (J. Clin. Meth. 25,97-99, 1987), except that fungizone was not included in the medium (seeSchinazi, et al., Antimicrob. Agents Chemother. 32, 1784-1787 (1988);Antimicrob. Agents Chemother., 34: 1061-1067 (1990)).

[0082] On day 6, the cells and supernatant were transferred to a 15 mltube and centrifuged at about 900 g for 10 minutes. Five ml ofsupernatant were removed and the virus was concentrated bycentrifugation at 40,000 rpm for 30 minutes (Beckman 70.1 Ti rotor). Thesolubilized virus pellet was processed for determination of the levelsof reverse transcriptase. Results are expressed in dpm/ml of sampledsupernatant. Virus from smaller volumes of supernatant (1 ml) can alsobe concentrated by centrifugation prior to solubilization anddetermination of reverse transcriptase levels.

[0083] The median effective (EC₅₀) concentration was determined by themedian effect method (Antimicrob. Agents Chemother. 30, 491-498 (1986).Briefly, the percent inhibition of virus, as determined frommeasurements of reverse transcriptase, is plotted versus the micromolarconcentration of compound. The EC₅₀ is the concentration of compound atwhich ther is a 50% inhibition of viral growth.

[0084] Mitogen stimulated uninfected human PBM cells (3.8×10⁵ cells/ml)were cultured in the presence and absence of drug under similarconditions as those used for the antiviral assay described above. Thecells were counted after six days using a hemacytometer and the trypanblue exclusion method, as described by Schinazi et al., AntimicrobialAgents and Chemotherapy, 22(3), 499 (1982). The IC₅₀ is theconcentration of compound which inhibits 50% of normal cell growth.

EXAMPLE 3 Anti-HIV Activity of β-L-(2′ or 3′)-A-5-FddC

[0085] The anti-HIV activity of L-2′-A-5-FddC and L-3′-A-5-FddC wastested in CEM and PBM cells. The results are provided in Table 1. TABLE1 Antiviral Activity Cytotoxicity Selectivity Index Compound EC₅₀ (μM)IC₅₀ (μM) IC₅₀/EC₅₀ L-2′-A-5-FddC 3.90 >100 >30 (CEM) L-3′-A-5-FddC0.29 >100 >344 (CEM) L-2′-A-5-FddC 1.00 >100 >100 (PBM) L-3′-A-5-FddC0.05 >100 >2647 (PBM)

[0086] Preparation of Pharmaceutical Compositions

[0087] Humans suffering from any of the disorders described herein,including AIDS, can be treated by administering to the patient aneffective treatment amount of β-L-(2′ or 3′)-A-5-FddC as describedherein, or a pharmaceutically acceptable prodrug or salt thereof in thepresence of a pharmaceutically acceptable carrier or diluent. The activematerials can be administered by any appropriate route, for example,orally, parenterally, intravenously, intradermally, subcutaneously, ortopically, in liquid or solid form.

[0088] The active compound is included in the pharmaceuticallyacceptable carrier or diluent in an amount sufficient to deliver to apatient a therapeutically effective amount of compound to inhibit viralreplication in vivo, without causing serious toxic effects in thepatient treated.

[0089] By “inhibitory amount” is meant an amount of active ingredientsufficient to exert an inhibitory effect as measured by, for example, anassay such as the ones described herein.

[0090] A preferred dose of the compound for all of the above mentionedconditions will be in the range from about 1 to 50 mg/kg, preferably 1to 20 mg/kg, of body weight per day, more generally 0.1 to about 100 mgper kilogram body weight of the recipient per day. The effective dosagerange of the pharmaceutically acceptable prodrug can be calculated basedon the weight of the parent nucleoside to be delivered. If the prodrugexhibits activity in itself, the effective dosage can be estimated asabove using the weight of the prodrug, or by other means known to thoseskilled in the art.

[0091] The compound is conveniently administered in unit any suitabledosage form, including but not limited to one containing 7 to 3000 mg,preferably 70 to 1400 mg of active ingredient per unit dosage form. Aoral dosage of 50-1000 mg is usually convenient, and more typically 50to 500 mg.

[0092] Ideally the active ingredient should be administered to achievepeak plasma concentrations of the active compound of from about 0.2 to70 μM, preferably about 1.0 to 10 μM. This may be achieved, for example,by the intravenous injection of a 0.1 to 5% solution of the activeingredient, optionally in saline, or administered as a bolus of theactive ingredient.

[0093] The concentration of active compound in the drug composition willdepend on absorption, inactivation, and excretion rates of the drug aswell as other factors known to those of skill in the art. It is to benoted that dosage values will also vary with the severity of thecondition to be alleviated. It is to be further understood that for anyparticular subject, specific dosage regimens should be adjusted overtime according to the individual need and the professional judgment ofthe person administering or supervising the administration of thecompositions, and that the concentration ranges set forth herein areexemplary only and are not intended to limit the scope or practice ofthe claimed composition. The active ingredient may be administered atonce, or may be divided into a number of smaller doses to beadministered at varying intervals of time.

[0094] A preferred mode of administration of the active compound isoral. Oral compositions will generally include an inert diluent or anedible carrier. They may be enclosed in gelatin capsules or compressedinto tablets. For the purpose of oral therapeutic administration, theactive compound can be incorporated with excipients and used in the formof tablets, troches, or capsules. Pharmaceutically compatible bindingagents, and/or adjuvant materials can be included as part of thecomposition.

[0095] The tablets, pills, capsules, troches and the like can containany of the following ingredients, or compounds of a similar nature: abinder such as microcrystalline cellulose, gum tragacanth or gelatin; anexcipient such as starch or lactose, a disintegrating agent such asalginic acid, Primogel, or corn starch; a lubricant such as magnesiumstearate or Sterotes; a glidant such as colloidal silicon dioxide; asweetening agent such as sucrose or saccharin; or a flavoring agent suchas peppermint, methyl salicylate, or orange flavoring. When the dosageunit form is a capsule, it can contain, in addition to material of theabove type, a liquid carrier such as a fatty oil. In addition, dosageunit forms can contain various other materials which modify the physicalform of the dosage unit, for example, coatings of sugar, shellac, orother enteric agents.

[0096] The compound can be administered as a component of an elixir,suspension, syrup, water, chewing gum or the like. A syrup may contain,in addition to the active compounds, sucrose as a sweetening agent andcertain preservatives, dyes and colorings and flavors.

[0097] The compound or a pharmaceutically acceptable derivative or saltsthereof can also be mixed with other active materials that do not impairthe desired action, or with materials that supplement the desiredaction, such as antibiotics, antifungals, antiinflammatories, proteaseinhibitors, or other nucleoside or nonnucleoside antiviral agents.Solutions or suspensions used for parenteral, intradermal, subcutaneous,or topical application can include the following components: a sterilediluent such as water for injection, saline solution, fixed oils,polyethylene glycols, glycerine, propylene glycol or other syntheticsolvents; antibacterial agents such as benzyl alcohol or methylparabens; antioxidants such as ascorbic acid or sodium bisulfite;chelating agents such as ethylenediaminetetraacetic acid; buffers suchas acetates, citrates or phosphates and agents for the adjustment oftonicity such as sodium chloride or dextrose. The parental preparationcan be enclosed in ampoules, disposable syringes or multiple dose vialsmade of glass or plastic.

[0098] If administered intravenously, preferred carriers arephysiological saline or phosphate buffered saline (PBS).

[0099] In a preferred embodiment, the active compounds are prepared withcarriers that will protect the compound against rapid elimination fromthe body, such as a controlled release formulation, including implantsand microencapsulated delivery systems. Biodegradable, biocompatiblepolymers can be used, such as ethylene vinyl acetate, polyanhydrides,polyglycolic acid, collagen, polyorthoesters, and polylacetic acid.Methods for preparation of such formulations will be apparent to thoseskilled in the art. The materials can also be obtained commercially fromAlza Corporation.

[0100] Liposomal suspensions (including liposomes targeted to infectedcells with monoclonal antibodies to viral antigens) are also preferredas pharmaceutically acceptable carriers. These may be prepared accordingto methods known to those skilled in the art, for example, as describedin U.S. Pat. No. 4,522,811 (which is incorporated herein by reference inits entirety). For example, liposome formulations may be prepared bydissolving appropriate lipid(s) (such as stearoyl phosphatidylethanolamine, stearoyl phosphatidyl choline, arachadoyl phosphatidylcholine, and cholesterol) in an inorganic solvent that is thenevaporated, leaving behind a thin film of dried lipid on the surface ofthe container. An aqueous solution of the active compound or itsmonophosphate, diphosphate, and/or triphosphate derivatives is thenintroduced into the container. The container is then swirled by hand tofree lipid material from the sides of the container and to disperselipid aggregates, thereby forming the liposomal suspension.

[0101] This invention has been described with reference to its preferredembodiments. Variations and modifications of the invention, will beobvious to those skilled in the art from the foregoing detaileddescription of the invention. It is intended that all of thesevariations and modifications be included within the scope of thisinvention.

We claim:
 1. A method for the treatment of HIV infection in a hostcomprising administering an effective amount of aβ-L-(2′-azido)-2′,3′-dideoxy-5-fluorocytosine compound or apharmaceutically acceptable ester, salt or prodrug thereof of theformula:

wherein R is H, acyl, monophosphate, diphosphate, or triphosphate, or astabilized phosphate derivative (to form a stabilized nucleotideprodrug), and R′ is H, acyl, or alkyl.
 2. The method of claim 1, whereinR is H.
 3. The method of claim 1, wherein R is acyl.
 4. The method ofclaim 1, wherein R is monophosphate.
 5. The method of claim 1, wherein Ris diphosphate.
 6. The method of claim 1, wherein R is triphosphate. 7.The method of claim 1, wherein R is a stabilized phosphate derivative.8. A method for the treatment of HIV infection in a host comprisingadministering an effective amount of aβ-L-(3′-azido)-2′,3′-dideoxy-5-fluorocytosine compound or apharmaceutically acceptable ester, salt or prodrug thereof of theformula:

wherein R is H, acyl, monophosphate, diphosphate, or triphosphate, or astabilized phosphate derivative (to form a stabilized nucleotideprodrug), R′ is H, acyl, or alkyl.
 9. The method of claim 8, wherein Ris H.
 10. The method of claim 8, wherein R is acyl.
 11. The method ofclaim 8, wherein R is monophosphate.
 12. The method of claim 8, whereinR is diphosphate.
 13. The method of claim 8, wherein R is triphosphate.14. The method of claim 8, wherein R is a stabilized phosphatederivative.